1. Field of the Invention
The present invention relates to a novel generator and a method of manufacturing the generator. More particularly, the present invention relates to a generator having a rotor coil end support suitable for a large-capacity generator, and a method of manufacturing the generator.
2. Description of the Related Art
Patent Document 1 (JP,A 8-205447) discloses a technique of forming a bind-underlying insulation over a rotor end portion of a generator by impregnating laminated insulating sheets, each of which comprises a polyimide film and a mica sheet bonded to each other, with an epoxy resin, and then forming a bind ring made of a nonmagnetic piano wire on the bind-underlying insulation. Also, Patent Document 2 (JP,A 7-184338) discloses a technique of forming a bind member made of chemical fibers in a tape-like shape over a rotor end portion of a generator. Further, Patent Document 3 (JP,A 6-98492) discloses a technique of forming a bind-underlying insulation made of a prepreg impregnated with a thermosetting resin, and then forming a bind ring on the bind-underlying insulation.
More specifically, the rotor end portion of the generator includes an iron core, a metallic support, a coil, etc. Because power is generated with the rotor rotating at a high speed during operation, large centrifugal forces are imposed on the iron core, the metallic support, the coil, etc. with the rotation. Therefore, stresses are loaded on the coil, whereupon the coil is deformed to bend outward in the radial direction. The coil is embedded in an insulator so as to resist the stresses. However, if the coil is deformed beyond the allowable strain or stress of the insulator, this leads to a possibility that the insulator is broken and a short-circuiting occurs between the coil and the iron core or a ground potential portion, such as the metallic support, thus resulting in damage of the rotor. In the worst case, the operation of the generator is disabled.
To cope with such a situation, as disclosed in Patent Documents 1-3, it is proposed so far to prevent the deformation of the coil by fitting the bind (ring) over the coil end portion while applying a tension to it so that the coil is firmly bound to the metallic support. The bind is formed of a metallic bind wire or a member prepared by impregnating non-metallic fibers with a setting resin and then hardening the resin.
The metallic bind wire is formed of a nonmagnetic piano wire or another suitable wire and is wound over the coil end portion with a strong tension applied so as to endure centrifugal forces generated based on the weight of the coil end portion and the rotation of the rotor and to be kept from loosening even under vibrations, etc.
In the case using the non-metallic fibers, the fibers are arrayed side by side to have a relatively large width and are impregnated with a setting resin into the form of a tape. This tape is wound over the coil end portion from the core side to the coil end in the axial direction of the generator while a strong tension is applied to the tape.
Because of the necessity of increasing the bind tension as the centrifugal force generated due to the rotation increases, however, the applied tension has been recently increased with an increase in output and size of the generator, and at the time of winding the bind wire or the tape to form the lowermost underlying layer, a bind winding machine is operated nearly at its maximum output in many cases. Application of such an increased load may give rise to the problem that, when the bind is successively wound in plural layers, lower layers are collapsed and cannot maintain a predetermined shape in the step of winding upper layers.
Further, the tension applied to the bind is gradually reduced with the lapse of time due to stress relaxation. In addition, the bind tension is also reduced with creep deformations of the coil fixedly bound by the bind, a dimension adjusting material, the bind itself, etc., which are all subjected to compressive loads.
If the bind tension is reduced in such a way, those coil end components are deformed to larger extents and the load imposed on the insulator supporting the coil is increased. This may increase deterioration with the lapse of time and shorten the life of the insulator. In spite of the design life of the insulator being not yet expired, the bind tension is so reduced as to allow slipping-off of the bind, thus resulting in a possibility that the rotor is immediately broken.
Particularly, in consideration of the centrifugal force increasing with a larger output capacity of the generator, a bind tape formed by impregnating nonmetallic fibers having high specific strength with a setting resin and hardening the impregnated fibers has been recently used in many cases. Because the stress relaxation and creep deformation of the bind using such a member are generally larger than those of the metallic bind, the above-mentioned problems become more serious.